[SYCL][ABI-break] Promote extended CG/handler members

[sergey-semenov]

Several new members were added to CG/handler via the extended member workaround. This patch promotes them to actual fields of those classes now that the ABI can be broken.

[sergey-semenov]

I'm planning to remove the extended member mechanism in a separate follow-up PR, just so it would be easier to recover it if we need to add new members to CG classes in the future.

[sergey-semenov]

@smaslov-intel Could you please review?

[sergey-semenov]

@steffenlarsen Could you please merge this one?

[sergey-semenov]

Looks like this introduced a post-commit failure, looking into it